The effects of slaughter age and restricted feeding on growth, carcass and meat quality traits of dairy breed lambs

Abstract

This experiment aimed to investigate the possibility to raise the carcass weight of lambs of dairy breed and produce low-fat meat by increasing the slaughter age and applying strategies to reduce feeding level. At 35d of age, 70 weaned lambs of Valle del Belice breed were divided into 2 groups and adapted to housing in multiple boxes and experimental diets over a 10-d period. The groups received ad libitum pelleted alfalfa hay and concentrates differing in the 20% inclusion of durum wheat bran (0WB, 20WB) used to reduce cost and energy level. After 45d of experiment, both groups were divided into 3 subgroups; 2 of them with 15 lambs were slaughtered at 90d of age (90L), whereas the other 4 subgroups received the same concentrates ad libitum (120L) or restricted at 75% of ad libitum intake (120R) for 30d until slaughter at 120d of age. Feed intake and live weight of lambs were regularly measured. At slaughter, carcass traits and tissue components of hind leg were recorded. Longissimus dorsi (LD) meat was evaluated for pH, colour, thawing and cooking losses, WB shear force and sensory properties in triangle tests. In both phases, 45-90d and 90-120d of age, the diet did not influence feed intake and growth of lambs fed ad libitum (90L and 120L), whereas under feed restriction the lambs fed 20WB showed a reduction in weight gain than 20R lambs fed 0WB (105 vs. 170 g/d, P≤0.05). In all production systems, the diet did not affect the carcass weight (12.6 vs. 12.4; 14.7 vs. 13.7; 15.6 vs. 14.9 kg for 0WB vs. 20WB in 90L, 120R and 120L), whereas the 20WB diet reduced carcass yield of 120R lambs (52 vs. 56 %, P≤0.01). The simultaneous feed and energy restriction for 120R lambs fed 20WB diet resulted in the lowest performance. The fat deposition, as perirenal and pelvic fat and adipose tissue of hing leg, increased from 90L to 120R, and to 120L lambs, regardless of diet. The LD traits were affected by the production system, since 90L lambs showed higher water losses, and lower tenderness and red colour than older lambs. At triangle tests, the panellists perceived significantly the differences due to diet for 90L and 120R meat, and the effect of feeding level. Thus, increasing the slaughter age of dairy breed lambs from 90 to 120 d of age lead to the production of heavier carcasses with improvements in meat quality in terms of tenderness and reduced water losses, especially due to a higher but moderate fat content, also when lambs were exposed to a 75% restricted feeding.